Specifications

Chapter 1 – Introduction
Multi-Tech Systems, Inc. AT Commands for EDGE Modems (S000371B) 17
For most of these messages, the ME needs to be configured whether or not to send a URC. Depending on the AT
command, the URC presentation mode can be saved to the user defined profile (see AT&W), or needs to be
activated every time you reboot the ME. Several URCs are not user definable, such as “^SYSSTART”, “^SYSSTART
<text>”, “^SHUTDOWN”.
If autobauding is enabled (as factory default mode or set with AT+IPR=0), URCs generated after restart will be output
with 57600 bps until the ME has detected the current bit rate. The URCs “^SYSSTART”, “^SYSSTART
<text>”, however, are not presented at all. For details please refer to Section 4.9.1, Autobauding. To avoid problems
we recommend to configure a fixed bit rate rather than using autobauding.
1.7.1 Communication between Customer Application and Multi-Tech Wireless
Modem
Leaving hardware flow control unconsidered the Customer Application (TE) is coupled with the Multi-Tech wireless
modem (ME) via a receive and a transmit line.
Since both lines are driven by independent devices, collisions may (and will) happen; i.e., while the TE issues an AT
command, the Multi-Tech wireless modem starts sending an URC. This will probably lead to the TE’s
misinterpretation of the URC being part of the AT command’s response.
To avoid this conflict the following measures must be taken:
• If an AT command is finished (with “OK” or “ERROR”) the TE shall always wait at least 100 milliseconds before
sending the next one.
This gives the Multi-Tech wireless modem the opportunity to transmit pending URCs and get necessary service.
Note that some AT commands may require more delay after “OK” or “ERROR” response, refer to the following
command specifications for details.
• The TE shall communicate with the Multi-Tech wireless modem using activated echo (ATE1); i.e., the Multi-Tech
wireless modem echoes characters received from the TE.
Hence, when the TE receives the echo of the first character “A” of the AT command just sent by itself it has
control both over the receive and the transmit paths.